Comparative analysis of fusariotoxins occurrence

In the field, plants are naturally in contact with various moulds, the most frequent one is Fusarium. Fusariosis is a common disease on cereals mainly affecting the cob and often caused by F. graminearum, F. culmorum, 
F. poae and F. avenaceum. As for all fungi, Fusarium growth depends on moisture level (22-25% humidity in the plant) and temperature (>15°C). Some cultivation methods have been identified for their impact on Fusarium development, like crop rotation. For instance, growing corn grain after a corn harvest increases the risk of deoxynivalenol occurrence in the crop, as the crop wastes are also contaminated with Fusarium and carry the fungi from one year to another. That’s also why no-till farming highly increases the risk of Fusarium development as crop wastes won’t be ploughed under, remaining on the field’s surface and contaminating the next crop (Gourdain et al, 2008). These practices are much more effective if all the farmers in an area apply them, as they help to reduce mould spores spreading by wind or rain. Selecting grain varieties that are resistant to Fusarium helps to control the risk on the crop, but this criterion is not always well documented for all types of seeds. Field application of fungicides can limit the development of some fungi in field but is not always feasible, like on the corn plant due to the height of the plants (Kharbikar et al, 2015). 
The mould itself is not a threat to the animal, but in stressful conditions Fusarium produces secondary metabolites: mycotoxins. All factors that alter the mould development can provoke the production of mycotoxins. For instance, it was observed that Fusarium proliferates between 25 and 30°C without producing any mycotoxins, whereas when the temperature drops to 0°C one part of the mould will produce high levels of mycotoxins. Also changes in humidity can affect the production of mycotoxins. As a consequence, grains are often contaminated with fusariotoxins like trichothecenes (DON), zearalenone and fumonisins, with variable levels of contamination depending on climate, cultivation methods, etc.

Study to identify variable fusariotoxin occurrence

Fusariotoxins occurrence and concentration in grains are variable among raw materials because of the different crop systems, as shown by the SCOOP survey in 2003. A study was carried out to identify the occurrence of fusariotoxins in the 3 main cereals used by the feed industry:

1. wheat,
2. barley and
3. different types of corn materials.

The study uses the Labocea database composed of chromatography analyses run with LC MS/MS from 2013 to 2015. 24 fusariotoxins are tested in each analysis. The percentage of positive samples (> LOQ) and the median level of contamination (ppb) per mycotoxin are the 2 main criteria used. In order to avoid any geographical interactions, samples from 1 restricted area only (France) are considered:

• wheat (n=274),
• barley (n= 104),
• dry corn grain (n=337),
• humid corn grain (n= 119) and
• corn silage (n= 557).

As the samples were not randomly selected, the absolute values of this study should not be considered as reference values but as relative values to better understand the risk by mycotoxin and by raw material.

Data shows that corn materials are more poly-contaminated than wheat and barley (per sample, on average 7 fusariotoxins are positive for corn materials, 2 for wheat and 3 for barley; Figure 1). As a consequence the percentage of positive samples for each mycotoxin is more important in corn materials than in other cereals. Deoxynivalenol (DON) is the most frequent fusariotoxin (>90% of positive samples, Figure 2) and major fusariotoxin in all types of feed materials. However its median level of contamination is far higher for corn silages (1,090 ppb) than wet corn (980 ppb) than corn grain (720 ppb) than wheat (215 ppb) and barley (75 ppb). The levels of 15-O-acetyl DON, zearalenone (ZEA) and fumonisins are also significantly higher for corn grain (respectively 153; 135 and 345 ppb) than for wheat (respectively 15, 25 and 50 ppb) and barley (respectively 20, 25 and 30 ppb) (Figure 3). The different cropping parameters (time of harvest, use of fungicide, etc) between corn and straw cereals could explain the important differences observed in fusariotoxins occurrence.

When focusing only on straw cereals, wheat shows higher median contamination in DON, T-2 toxin and fumonisins (respectively 215, 35 and 50 ppb) than barley (respectively 75, 10 and 30 ppb), whereas barley is more often contaminated in DON acetyl forms (40.4% in 15-O-acteyl and 17.3% in 3-O-acetyl DON) than wheat (5.8% in 15-O-acteyl and 16.4% in 3-O-acetyl DON). This is in accordance with Rishi et al. (2008) findings showing that all barley isolates had the 15-O-acetyl DON chemotype whereas only 62% of wheat 
isolates had it.

Fusariotoxins in corn raw materials

If focusing only on corn, the profiles of fusariotoxins contamination are very similar among corn raw materials whereas the level of median contamination depends on the type of corn material. Deoxynivalenol acetyl forms (15-O-acetyl and 3-O-acetyl DON) contaminations are similar for all types of corn materials. Nevertheless, nivalenol (NIV) median level in corn silage is four times higher than in corn grain (290 ppb vs 68 ppb, respectively). On the contrary, corn grain has a higher median sum of fumonisins (320 ppb) than corn silage (40 ppb) and wet corn (68 ppb). 
An important feature of DON contamination in corn is that the levels of this mycotoxin can be even higher in the leaves and stalk than in the cob, whereas fumonisins are only produced on ear rot (Oldenburg et al., 2005). This explains why corn silage is more contaminated in DON whereas corn grain is more contaminated in fumonisins. Zearalenone (ZEA) occurrence is similar in all types of corn materials with contamination levels far lower than for DON (median level: < 200 ppb for ZEA; > 700 ppb for DON). Regarding type-A trichothecenes the profiles of contamination are equivalent for all types of corn materials apart for one metabolite (MAS) which is more often present in corn silage (66.4%) than in wet corn (32.8%) and in corn grain (11%).

Such view and understanding allows a better management of mycotoxin risk by the feed industry. Indeed, these data can help feed producers to adjust their quality control plan and to optimise their use of mycotoxin binder in feeds. Used at the right dosage, a wide spectrum toxin binder will prevent any loss in performance at the best cost effectiveness.